Spin down and oscillations in 4U 1907+09: a retrograde disk?

Date

1999-01-01

Author

Zand, JJMI
Strohmayer, TE
Baykal, Altan

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X-ray observations of the accretion-powered X-ray pulsar 4U 1907+09, obtained during February 1996 with the Proportional Counter Array on the Rossi X-ray Timing Experiment (RXTE), have shown interesting features of which three are: 1) a flare occurred lasting at least a few hours and close to the time of apastron; 2) the spin down rate, when measured since the pulsar discovery in 1983, is within 8% equal to a value of (P)over dot(pulse) = +0.225 s yr(-1), this suggest that the pulsar is in a monotonous spin down mode; 3) transient similar to 18 s oscillations appeared during the flare. The oscillations may be interpreted as Keplerian motion of an accretion disk near the magnetospheric radius. This, and the notion that the co-rotation radius is much larger than any conceivable value for the magnetospheric radius (because of the long spin period), renders it unlikely that this pulsar spins near equilibrium like is suspected for other slowing accreting X-ray pulsars. We suggest as an alternative that perhaps the frequent occurrence of a retrograde transient accretion disk may be consistently slowing the pulsar down. Further observations of flares can provide more evidence of this.

Subject Keywords

Pulsar, Ray, Quasi-periodic oscillations

URI

https://hdl.handle.net/11511/46585

Journal

NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS

DOI

https://doi.org/10.1016/s0920-5632(98)00213-8

Collections

Department of Physics, Article

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Recent X-ray measurements of the accretion-powered pulsar 4U 1907+09 in't Zand, JJM; Baykal, Altan; Strohmayer, TE (IOP Publishing, 1998-03-20) X-ray observations of the accreting X-ray pulsar 4U 1907 + 09 obtained during 1996 February with the Proportional Counter Array onboard the Rossi X-Ray Timing Explorer (RXTE) have made possible the first measurement of the intrinsic pulse period (P-pulse) since 1984: P-pulse = 440.341(-0.017)(+0.012) s. 4U pulse 1907 + 09 is in a binary system with a blue supergiant. The orbital parameters have been solved, which enables us to correct a measurement of P-pulse obtained in 1990 with Ginga for orbital delay ef...
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Citation Formats

J. Zand, T. Strohmayer, and A. Baykal, “Spin down and oscillations in 4U 1907+09: a retrograde disk?,” NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS, pp. 224–227, 1999, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/46585.